Kinetic energy absorption methods

ABSTRACT

A kinetic energy absorptive composite article includes a first ply and a plurality of inherently straight first fibers contained in the first ply. First length portions of the first fibers are arranged with first localized ripples that deviate from and return to individual first routes of respective first length portions. The article includes a second ply parallel to the first ply, a plurality of inherently straight second fibers contained in the first ply or the second ply, and a matrix material at least partially encapsulating the first and second plies. Second length portions of the second fibers are arranged without localized ripples or with second localized ripples that deviate from individual second routes of respective second length portions to a lesser extent than the first localized ripples and return to the individual second routes. The second routes are substantially parallel to the first routes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims priority to, U.S. patentapplication Ser. No. 15/904,955, filed on Feb. 26, 2018, issued as U.S.Pat. No. 10,493,720, and entitled “Kinetic Energy Absorptive CompositeArticle and Absorption Method,” which is a divisional of, and claimspriority to, U.S. patent application Ser. No. 15/904,955, published asU.S. Patent Publication No. 2019/0263088, filed on Feb. 26, 2018, andentitled “Kinetic Energy Absorptive Composite Article and AbsorptionMethod,” the contents of each of which are hereby incorporated byreference in their entirety.

BACKGROUND

Aircraft, spacecraft, and other structures may be impacted by variousforeign objects. Examples include debris (such as tire treads, rocks,etc.), hail, micrometeoroids, etc. Breach of the structure couldsignificantly damage internal components and effect structuralintegrity, even resulting in catastrophic loss of aircraft, spacecraftand other vehicular structures.

Aircraft, spacecraft, and other vehicular structures that carry fuel mayexperience a breach of fuel containment during a ground impact. Avariety of self-sealing fuel bladders and impact containment structuresexist with the goal of resisting breach of fuel containment during suchevents. Known fuel bladders and containment structures designed withsuch goals in mind are often made of either fabrics or unidirectionalfibers. However, a desire exists to reduce the mass of fuel bladders andcontainment structures while still providing the same breach resistanceor increasing breach resistance.

Accordingly, it will be appreciated that more efficient materials toreduce breach of structures would be beneficial for aircraft,spacecraft, and other vehicular structures subject to impact by foreignobjects. More efficient materials exhibit a higher specific strength(strength/density), sometimes referred to as the strength-to-weightratio. Similarly, more efficient breach resistant fuel bladders andcontainment structures would be beneficial. Materials with higherefficiency maintain or increase resistance to breach with less mass ofthe structural material compared to known structural materials.

SUMMARY

A kinetic energy absorptive composite article includes a first ply and aplurality of inherently straight first fibers contained in the firstply. Individual first fibers have a cross-sectional shape that issubstantially constant along a first length portion of the individualfirst fibers. The first length portions are aligned along substantiallyparallel first routes within the first ply. The first length portionsare also arranged with first localized ripples in the first lengthportions that deviate from and return to individual first routes ofrespective first length portions. The article includes a second plyparallel to the first ply, a plurality of inherently straight secondfibers contained in the first ply or the second ply, and a matrixmaterial at least partially encapsulating the first and second plies.Individual second fibers have a cross-sectional shape that issubstantially constant along a second length portion of the individualsecond fibers. The second length portions are aligned alongsubstantially parallel second routes within the respective first ply orsecond ply. The second length portions are arranged without localizedripples in the second length portions or with second localized ripplesin the second length portions that deviate from individual second routesof respective second length portions to a lesser extent than the firstlocalized ripples and return to the individual second routes. The secondroutes are substantially parallel to the first routes.

A kinetic energy absorptive composite article includes a first ply and aplurality of inherently straight first fibers contained in the firstply. Individual first fibers have a cross-sectional shape that issubstantially constant along a first length portion of the individualfirst fibers. The first length portions of the first fibers are alignedalong substantially parallel first routes within the first ply. Thefirst length portions are also arranged with a first pattern referencedto individual first routes of respective first length portions. Thearticle includes a second ply parallel to the first ply, a plurality ofinherently straight second fibers contained in the first ply or thesecond ply, and a matrix material at least partially encapsulating thefirst and second plies. Individual second fibers have a cross-sectionalshape that is substantially constant along a second length portion ofthe individual second fibers. The second length portions are alignedalong substantially parallel second routes within the respective firstply or second ply. The second length portions are arranged with a secondpattern referenced to individual second routes of respective secondlength portions in a manner different from the first pattern. The secondroutes are substantially parallel to the first routes. The articlefurther includes a means for progressively loading the first and secondfibers when the composite article receives a sufficient force fromkinetic energy.

A kinetic energy absorption method provides a composite articleincluding a first ply, a plurality of inherently straight first fiberscontained in the first ply, a second ply parallel to the first ply, aplurality of inherently straight second fibers contained in the firstply or the second ply, and a matrix material at least partiallyencapsulating the first and second plies. Individual first fibers have afirst length portion providing a plurality of first length portionsaligned along substantially parallel first routes within the first ply.The plurality of first length portions are arranged with first localizedripples in the first length portions that deviate from and return toindividual first routes of respective first length portions.

Individual second fibers have a second length portion providing aplurality of second length portions aligned along substantially parallelsecond routes within the respective first ply or second ply. Theplurality of second length portions are arranged without localizedripples in the second length portions or with second localized ripplesin the second length portions that deviate from individual second routesof respective second length portions to a lesser extent than the firstlocalized ripples and return to the individual second routes. The secondroutes are substantially parallel to the first routes.

The method includes progressively loading the first fibers and thesecond fibers when the first and second plies receive a sufficient forcefrom kinetic energy by:

irreversibly shearing the matrix material or breaking adhesion of thematrix material to at least a part of individual second fibersaccompanied by plastically deforming or causing failure of the secondfibers; and

irreversibly shearing the matrix material or breaking adhesion of thematrix material to at least part of the first localized ripplesaccompanied by pulling out at least part of the first localized rippleswithout failure of the first fibers.

The features, functions, and advantages that have been described can beachieved independently in various embodiments or may be combined in yetother embodiments further details of which can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are described below with reference to the followingaccompanying drawings.

FIG. 1 shows a side view of a fuel bladder and its impact with theground.

FIG. 2 shows a diagram of fibers in a ply before and after applyingfiber stress.

FIG. 3 shows a diagram of rippled fibers in a ply before and afterapplying fiber stress.

FIG. 4 is a chart of hypothetical fiber stress after impact for thefibers in FIGS. 2 and 3.

FIG. 5 is a side view of an object impacting a series of plies.

FIG. 6 is a side view of a series of plies containing rippled fibers.

FIG. 7 is a side view of an object impacting a series of plies withrippled fibers.

FIGS. 8-11 are top views of various single plies with rippled fibers.

FIGS. 12-15 are side views of various series of plies containing rippledfibers.

FIG. 16 is a perspective view of a spherical object with rippled fibersaligned along its surface.

FIGS. 17A, 17B, and 17C are sequential side views of an object impactinga series of layers.

DETAILED DESCRIPTION

During a ground impact event, liquid fuel in a fuel bladder produces ahydrodynamic ram that may cause fibers to undergo very sharp impulseloading, potentially causing failure of the bladder wall. Known bladdershave been very robustly designed to overcome a failure, but robustlydesigned bladder walls are heavy. FIG. 1 shows a fuel bladder 10 afalling to the ground and being distorted upon impact to yield animpacted fuel bladder 10 b. Distortion of the walls in impacted fuelbladder 10 b shows one example of the impulse loading that fibersundergo from the hydrodynamic ram caused by contained fuel. Impactcontainment structures surrounding fuel bladders may be provided andsimilarly designed very robustly to meet performance criteria for animpact. A robust design might include very tough materials, such asKEVLAR or other synthetic fibers, and also may be heavy in keeping withthe robust design.

The methods and apparatuses described herein allow progressive fiberloading and selective fiber failure as a mechanism for absorbing thekinetic energy applied by an impulse due to a ground impact. As such,the peak load on individual fibers may be reduced, allowing structurewalls to be more efficiently designed and resulting in a lighterstructure while maintaining performance. The same concept permits designof structures subject to impact by foreign objects, such that kineticenergy of objects may be absorbed and the peak load on individual fibersreduced.

Ripples in the fibers constitutes one design feature to assist with suchobjectives. Other assistive design features are described herein. Bymaking at least some of the fibers non-straight, curves in the fiberwithin a ply can pull out during an impact event, permitting the fiberto change position prior to reaching its failure strain. As a result,targeted delamination of a composite and selective shearing of somefibers allows kinetic energy absorption without breach.

FIG. 2 shows fibers 20 a before loading from a kinetic impulse when nofiber stress is applied and corresponds to the initial state in FIG. 4for straight fibers. FIG. 2 also shows loaded fibers 20 b after 5arbitrary units of time when fiber stress reaches 60 arbitrary units ofstress and failure occurs. FIG. 4 shows the hypothetical rise in fiberstress over 5 time units followed by failure.

In comparison, FIG. 3 shows fibers identical to fibers 20 a arranged asrippled fibers 30 a before loading when no fiber stress is applied andcorresponds to the initial state in FIG. 4 for rippled fibers. After 5time units, loaded rippled fibers 30 b are shown with some of theripples pulled out. That is, the ripples are leveled somewhat orsmoothed, with decreased amplitude and/or increased period. “Amplitude”refers to the height change in units of distance between a peak and anadjacent trough in the ripples, analogous to peak-to-peak amplitude forelectrical oscillations. “Period” refers to the spatial distance overwhich a single cycle of the ripples extends in units of distance percycle, analogous to the period for electrical oscillations. Althoughabout 9 stress units exist in loaded rippled fibers 30 b after 5 timeunits, the fiber stress is much less in comparison to the fiber stressafter 5 time units for loaded fibers 20 b in FIG. 2. Loading continuesto increase and, after 15 time units, further loaded rippled fibers 30 cshow the ripples further pulled out, amplitude further decreased, andperiod further increased with more leveling or smoothing of the ripples.In FIG. 4, fiber stress is decreasing at 15 time units with peak stressreached at about 14 time units, but being insufficient to fail thefibers.

The loading of fibers in FIGS. 2 and 3 may be realized when a fuelbladder containing liquid impacts the ground, as in FIG. 1. The liquidpushes against the sidewalls of the bladder, causing outward pressure atthe bottom of the bladder. In a relatively stiff bladder, the outwardpressure at the bottom of the bladder rises rapidly and can causefailure of the bladder due to the high mechanical load. To mitigatefailure in such circumstance, the kinetic energy of the outward pressurecould be absorbed within the bladder walls during deformation usingrippled fibers, such as in FIG. 3. The outward pressure pulls out theripples in rippled fibers 30 a which absorb the kinetic energy in theprocess. This is not to say that the fibers necessarily retractelastically after loading. Indeed, a fuel bladder containing rippledfibers 30 a may plastically deform during a ground impact event, butnonetheless reduce fiber failure, containing the fuel.

Similar principles apply in mitigating consequences of an objectimpacting a structure. FIG. 5 shows fibers 50 arranged in a series ofplies where the x direction represents a lateral dimension along thefiber lengths and the z direction represents the vertical dimensionthrough the thickness of the combined plies. FIG. 5 shows a side view ofone fiber in each ply. Object 52 impacts fibers 50 in thethrough-thickness direction, or vertical dimension. FIG. 5 shows thatmany of fibers 50 failed during the impact of object 52 and were shearedahead of object 52 as it traveled into the thickness.

The shearing of fibers 50 absorbs some of the kinetic energy of object52 and helps to avoid breach of a structure by object 52. Even so,avoiding breach requires a greater mass of fibers and matrix compared tothe methods and apparatuses described herein. Known damage resistantstructures are made using mostly composites with a single type of fiberin a simple cross-plied layup. These layups might stop an object throughmechanisms similar to those described herein, but the extent andlocation of the different mechanisms is not controlled. The methods andapparatuses herein provide a way of causing delaminations and shearfailures at specific locations as well as influencing the shape ofdeformations as a damage resistant structure slows an impacting object.By causing deformations and shear failures to occur at desired locationsand in desired modes, the structure may be more efficient and, thus,lighter in comparison to known structures without such features.

FIG. 6 shows rippled fibers 60 a arranged in a series of plies. Again,the x direction represents the lateral dimension along the lengths offibers 60 a and the z direction represents the vertical dimensionthrough the thickness of the combined plies. Fibers 60 a are alignedalong substantially parallel routes with the location of one such routebeing identified by arrow 64. The existence of parallel routes forfibers 60 a is consistent with stacking plies to form the combinedplies. Cross plies orthogonal to rippled fibers 60 a may be used in themethods and apparatuses herein, but are not shown for simplicity. Also,methods and apparatuses herein may include plies at other angles, suchas 10°, 30°, 45°, 60°, etc., but are also not shown for simplicity. Forexample, one or more plies of 10° fibers may be included. In anothermethod or apparatus, one or more plies of 30° fibers may be included. Inyet another method or apparatus, one or more plies of 60° fibers may beincluded. Fibers 60 a deviate from and return to individual routes,creating the rippled form shown. The routes extend in the same directionin each ply, designating substantially parallel routes for the fibers.It will be appreciated from the discussion herein that a substantiallyparallel route might deviate in a de minimis amount from a perfectlyparallel route while still providing the benefits of the methods andapparatuses described herein.

FIG. 3 shows how ripples may pull out of a rippled fiber when outwardpressure is applied (see FIG. 1) at the bottom of a fuel bladder duringan impact with the ground. FIG. 7 shows a more focused impact, such aswhen object 52 impacts fibers 60 a. Loaded rippled fibers 60 b absorbthe kinetic energy of object 52 instead of shearing as in FIG. 5. Whenobject 52 impacts the first of rippled fibers 60 a, the ripples of thefiber begin to pull out as object 52 progresses into the thickness andcontacts the second, third, and successive fibers, progressively pullingout the ripples of each rippled fiber.

In the hypothetical of FIG. 7, object 52 impacts the fibers of fiveplies without shearing any of rippled fibers 60 a. The ripples allowfibers 60 b to dislocate from their original position as theyprogressively load without failing. The impact event in FIG. 7 involvesmore fiber simultaneously, compared to sequentially, as in FIG. 5. Thus,fibers 60 b absorb more energy compared to fibers 50. Fibers 50 cannotdislocate from their original position and, consequently, load rapidlyand fail rapidly and locally as object 52 impacts successive fibers.

Rippled fibers 60 a (as well as rippled fibers 30 a in FIG. 3) are shownwith a sinusoidal path, meaning the path that the ripples follow as theydeviate from and return to individual routes of the fibers. However,other options are possible for the ripples. For example, ripples neednot be sinusoidal. Also, ripples need not deviate periodically, that is,at regular intervals, or in any consistent pattern. Ripples may deviatein some manner different from the sinusoidal path in FIGS. 3 and 6 whilestill permitting the ripples to pull out and to absorb kinetic energyduring an impact event, whether impacted by an object or impacting withthe ground. Among others, suitable examples additional to those shown inthe Figures include a helix or a flattened helix.

On a related note, fibers 60 a are shown deviating in the z direction,or vertical dimension representing the thickness of the combined plies.If the plies including fibers 60 a are planar, then it will beappreciated that fibers 60 a deviate out-of-plane for the plane definedby each ply. Even so, a similar effect of absorbing kinetic energy canbe realized when fibers deviate in-plane for the plane defined by aparticular ply. Various configurations for fiber deviation are describedbelow.

FIG. 7 could be considered to show object 52 halted in its progressionthrough the thickness of combined plies containing rippled fibers 60 b.FIG. 7 may instead be considered to show object 52 at a point along itspath continuing through the thickness. It is conceivable that object 52could impact each of fibers 60 b and continue past the thicknessboundary of the combined plies without causing failure of the structure.Such circumstance could arise when object 52 continues through thethickness and engages all seven plies shown in FIG. 7. Object 52 couldcontinue to pull out the ripples of fibers 60 b, eventually halting withall seven fibers intact, but the ripples pulled out to the extent thatthe position of object 52 extends past the seventh fiber.

The same circumstance could arise with any number of plies such that anobject impacts the full thickness of the combined plies. In such animpact event, the back layers of a structure may ultimately deform alongwith the front layers, depending on the thickness of the combined plies,while the impact event continues by pulling out the ripples of all thelayers at the same time. Thus, rippled fibers constitute oneconsideration in tailoring energy dissipation as a function of thedistance an object travels through the plies after impact. This allowscontrolling the force vs. distance used to stop the object.

Ripples may be formed using a variety of methods and apparatuses. Oneexample includes a crimping device, such as one with cogs, that crimpsfibers as the cogs turn and a fiber or a ply is fed through the crimpingdevice. Such ripples may be formed in-plane or out-of-plane. Also, a setof bars or clamping bars may be used to push alternating sections of afiber in opposite directions in a ply. Each section could be one-half ofa period for the ripples. Such ripples might be most effectively madein-plane.

In addition to ripples, several design considerations exist that mayassist in controlling kinetic energy absorption, accommodating a varietyof expected types of impact events. One such design considerationinvolves selecting fibers with different properties, such as failurestrain, modulus, strength, etc. These properties may be temperaturedependent and/or may vary with time during an impact event while astructure deforms. Largely, fiber composition determines failure strainand other mechanical properties, but fiber manufacturing methods mayalso play a role. Such properties are often well-defined for knownfibers and the most appropriate known fibers to achieve specified designgoals may be selected.

Conceivably, fibers of the same chemical composition could exhibitdifferent mechanical properties. Consequently, any references herein tofibers of different composition could be generalized to reference fibersof different mechanical properties, such as failure strain, even iffiber composition is the same.

In the context of the present document, failure strain is theengineering (i.e., nominal) strain at which a material fails. Also,“adhesion” refers to a widely-known property describing the tendency ofsurfaces to cling to one another. Additionally, “ductility” refers to awidely-known property wherein a material plastically deforms beforefailing, as contrasted with brittle materials. In some systems,ductility may be quantified as the percent elongation at failure.Further, “strength” refers to the ability of a material to avoid failurewhile withstanding an applied stress. In some systems, strength may bequantified as the ultimate tensile strength, meaning the maximumengineering (i.e., nominal) stress of the stress-strain curve. Stillfurther, “modulus” (i.e., “elastic modulus”) describes the ability of amaterial to resist elastic deformation. In some systems, modulus may bequantified as the slope of the stress-strain curve in the elasticregion. Failure strain, adhesion, ductility, strength, and modulus maybe measured by a variety of techniques known to those of ordinary skill.

FIGS. 8-15 show various configurations that each include two types offibers. Solid lines, such as for first fiber 80, represent a first typeof fiber while dashed lines, such as for second fiber 82, represent asecond type of fiber. First fibers 80 have a material composition incommon and second fibers 82 have a material composition in common thatis different from the first fibers' material composition. Likewise, inFIGS. 9-15, solid lines indicate first fibers with a common firstcomposition and dashed lines indicate second fibers with a common secondcomposition. Examples of known fiber materials includes nylon,polyethylene, aramid (e.g. KEVLAR), POM (polyoxymethylene, e.g. DELRIN),PTFE (polytetrafluoroethylene, e.g. TEFLON); PEEK(polyetheretherketone), polyesters (such as, PET (polyethyleneterephthalate) and others), PP (polypropylene), and PVA (polyvinylalcohol). Others are known as well. Although FIGS. 8-15 show two typesof fibers, it will be appreciated that more than two types of fiberscould be used to achieve a benefit in keeping with the designconsiderations described herein.

FIG. 8 shows a top view of rippled first fibers 80 and rippled secondfibers 82 with the x direction indicating a lateral dimension along thelength of the fibers while the y direction indicates a lateral dimensionacross the width of the combined fibers in a ply 88. First fibers 80 arealigned along substantially parallel first routes 84 within ply 88.Ripples deviate from and return to individual first routes 84 ofrespective first fibers 80. Second fibers 82 are aligned alongsubstantially parallel second routes 86 within ply 88. Ripples deviatefrom and return to individual second routes 86 of respective secondfibers 82. First routes 84 are substantially parallel to second routes86. Fibers 80 and 82 deviate to the same extent, for example, FIG. 8shows that the amplitude and period of the sinusoidal path is the samefor fibers 80 and 82. As mentioned, other types of periodic ornon-periodic deviations may be used in the methods and apparatusesherein.

FIG. 12 is similar to FIG. 8 in that first fibers 120 have a commonfirst composition and second fibers 122 have a common second compositiondifferent from the first composition. Also, fiber 120 in first ply 128is aligned along first route 124 in first ply 128. Fiber 122 in secondply 129 is aligned along second route 126 in second ply 129. Ripples infibers 120 and 122 deviate from their respective routes to the sameextent. While the x direction in FIG. 12 represents a lateral dimensionalong the fiber length, FIG. 12 differs from FIG. 8 in that the zdirection represents a vertical dimension through the thickness ofcombined plies that include fibers 120 and 122. FIG. 12 shows seven ofsuch plies. If ply 88 in FIG. 8 is planar, then ripples in fibers 80 and82 would be considered to deviate in-plane. If plies 128 and 129 in FIG.12 are planar, then ripples in fibers 120 and 122 would be considered todeviate out-of-plane.

Whether fibers are selected to deviate in- or out-of-plane mostlyinvolves two considerations. First, it is expected that in-planedeviations will be more manufacturable, that is, less technicallychallenging to produce. Second, opportunity might exist for fiberinteractions between plies with out-of-plane deviations. If ripplesdeviate out-of-plane from a ply, then ripples of adjacent pliespotentially interact to increase energy absorption through increasedfriction or other forces between plies.

Another way to describe the orientation of ripples in FIGS. 8 and 12involves a geometric surface defined by the fiber routes as a generalcase, regardless of whether plies are planar or curved. In FIG. 8, theripples deviating from and returning to first routes 84 are coextensivewith a geometric surface defined by first routes 84 within ply 88. InFIG. 8, ply 88 could be planar such that it may be said the ripplesdeviate in-plane. However, if ply 88 is not planar, it may still be saidthat the ripples are coextensive with a geometric surface defined byfirst routes 84 within ply 88. Similarly, the ripples in second fibers82 deviating from and returning to second routes 86 are coextensive withthe geometric surface defined by second routes 86 in ply 88.

Rippled second fibers 82 shown in FIG. 8 deviate in-plane with ply 88and with first routes 84 of first fibers 80. That is, routes 84 and 86are coplanar as well as parallel. In the event that ply 88 is notplanar, the ripples of second fibers 82 would be coextensive with thegeometric surface defined by first routes 84 for first fibers 80. Insuch a circumstance, it could be said that routes 86 also define thegeometric surface of ply 88. Consequently, both first route 84 andsecond route 86 define the geometric surface. This concept may befurther understood from the description below regarding FIG. 16.

FIG. 9 shows a top view of rippled first fibers 90 and rippled secondfibers 92 in a ply 98. The ripples of fibers 90 and 92 are not apparentfrom FIG. 9 since they deviate out-of-plane. The x direction in FIG. 9corresponds to a lateral dimension along the fiber lengths and the ydirection corresponds to a lateral dimension across the width of thecombined fibers in ply 98. Rippled first fibers 90 have a common firstcomposition and rippled second fibers 92 have a common secondcomposition that is different from the first composition. That is, thefibers and ply in FIG. 9 are identical to the fibers and ply in FIG. 8except for the out-of-plane deviation.

In effect, merely rotating ripples in fibers 80 and 82 of FIG. 8 to 90°around an axis corresponding to routes 84 and 86 turns the ripples todeviate out-of-plane, yielding the top view shown in FIG. 9. FIG. 9 doesnot show first or second routes of fibers 90 and 92 since they aresuperimposed over and could not be distinguished from the fibersthemselves. Nonetheless, such routes exist and are identical in positionto routes 84 and 86 in FIG. 8.

The concept of out-of-plane deviation applies when ply 98 is planar. Thegeneral case for both planar and curved plies would state that theripples of fibers 90 and 92 deviate from and return to their respectiveroutes and do not fully coextend with a geometric surface defined by theroutes of fibers 90 within ply 98. In other words, the ripples extendoutward from such a geometric surface. Ripples in FIG. 9 extendperpendicular to ply 98. However, the ripples could extend at differentangles, such as 10°, 30°, 45°, 60°, etc., and still be considered not tofully coextend with the geometric surface defined by the routes offibers 90.

FIGS. 10 and 11 show a further modification to plies compared to thosein FIG. 8, wherein second fibers do not include ripples or includeripples that deviate to a lesser extent. FIG. 10 is a top view of a ply108 where the x direction corresponds to a lateral dimension along thefiber lengths and the y direction corresponds to a lateral dimensionacross the width of the combined fibers in ply 108. Rippled fibers 100have a common first composition and rippled second fibers 102 have acommon second composition different from the first composition. Fibers100 are aligned along substantially parallel first routes 104 and fibers102 are aligned along substantially parallel second routes 106. Firstroutes 104 are parallel with second routes 106. In addition to having adifferent composition, ripples in fibers 102 deviate to a lesser extentthan ripples in fibers 100. Specifically, the period of fibers 102 istwice that of fibers 100. For each cycle in ripples of fibers 102, twocycles exist in ripples of fibers 100. The ripples of fibers 100 arecoextensive with a geometric surface defined by first routes 104 withinply 108. The ripples of second fiber 102 are also coextensive with thatgeometric surface. When ply 108 is planar, it could be said that fibers100 and 102 deviate in-plane.

FIG. 11 shows a top view of rippled first fibers 110 and second fibers112, which are not rippled, included in a ply 118. Ripples in firstfibers 110 deviate from and return to substantially parallel firstroutes 114. Second fibers 112 do not deviate from a fiber route, insteadbeing superimposed thereon since no ripples are in fibers 112. Routesfor fibers 112 are thus not shown in FIG. 11 as not distinguishable fromfibers 112. First route 114 and second fibers 112 are substantiallyparallel. The x direction corresponds to a lateral dimension along thefiber lengths and the y direction corresponds to a lateral dimensionacross the width of the combined fibers in ply 118. The ripples offibers 110 are coextensive with a geometric surface defined by firstroutes 114 within ply 118.

FIGS. 10 and 11 are useful to explain the concept of “path length.” Thepath lengths for fibers 100, 102, 110, and 112 are measured along thepaths that the fibers travel throughout their deviations. While all ofthe fibers have a “route” designating the direction of fiber travel, thefiber “paths” correspond to the specific position of the fiber itselfthroughout its deviations from the fiber route. Consequently, it will beappreciated that, between the fiber ends displayed in FIGS. 10 and 11,fibers 100 and 110 have the longest path length, fibers 102 have thenext longest path length, and fibers 112 have the shortest path length(with no deviations).

Accordingly, fibers 100/110, 102, and 112 possess differing abilities toabsorb kinetic energy during an impact event. Fibers 112 may only absorban amount of kinetic energy that is sufficient to plastically deform andfail fibers 112. The degree of plastic deformation varies by type offiber material. Brittle fibers fail after little or no deformation andmore ductile fibers fail after plastically elongating. Fibers 102 mayabsorb an amount of kinetic energy sufficient to pull out the ripples,plastically deform, and fail fibers 102. Fibers 100/110 may absorb agreater amount of kinetic energy, compared to fibers 102 and 112,sufficient to pull out the ripples of fibers 100/110 with the longestpath length, and plastically deform and fail such fibers. Each stage ofpulling out the ripples, plastically deforming the fiber, and failingthe fiber absorbs an amount of kinetic energy. Thus, the path lengths offiber deviations (as well as fiber failure strain) may be varied toaccommodate varying levels of kinetic energy absorption.

Path length may be selected by selecting both the amplitude and theperiod of ripples. For a given amplitude, increasing the period(distance per cycle) of ripples will decrease the path length. For agiven period, decreasing the amplitude (height change) of ripples willdecrease the path length. One fiber may deviate from its route to alesser extent than another fiber deviates from its route because of lessamplitude in ripples, greater period in ripples, or both. In otherwords, less deviation results in shorter path length.

FIGS. 10 and 11 incorporate the design consideration of differentcomposition among fibers as well as the design consideration of rippleswith different path lengths. However, it will be appreciated that fibersof the same composition could be used in FIGS. 10 and 11 such that onlythe design consideration of ripples with different path lengths isaddressed.

FIGS. 12-15 correspond with FIGS. 8-11, respectively, except that sevenplies are shown with the x directions corresponding to a lateraldimension along the fiber lengths and the z direction corresponding to avertical dimension through the thickness of the combined plies. FIGS.12-15 are the side views of a combination of plies with only one fiberin each ply being perceivable in the side views.

FIG. 12 shows a side view of first fiber 120 in a first ply 128 and asecond fiber 122 in a second ply 129. Ripples in first fiber 120 deviatefrom and return to a first route 124 within first ply 128. Ripples insecond fiber 122 deviate from and return to a second route 126 withinsecond ply 129. First route 124 and second route 126 are substantiallyparallel. It will be appreciated that the deviations of ripples in firstfiber 120 are out-of-plane when first ply 128 is planar. The ripples insecond fiber 122 are also out-of-plane. For the general case, theripples do not fully coextend with a geometric surface defined by firstroute 124 combined with additional first routes 124 (not shown) ofadditional first fibers 120 (not shown) within first ply 128, but notapparent from FIG. 12. The ripples in second fiber 122 are also notfully coextensive. Although FIG. 12 shows only one fiber in each ply, itwill be appreciated that plies include additional fibers. First fibers120 in first ply 128 have a first composition in common and secondfibers 122 in second ply 129 have a second composition in common thatdiffers from the first composition.

FIG. 13 is similar to FIG. 12 in all respects except for the orientationof fibers 120 and 122. Rotating rippled fibers 120 and 122 about theirrespective routes to 90° yields rippled fibers 130 and 132 that deviatein-plane with their respective plies 138 and 139 when planar. Theripples of fibers 130 and 132 are not apparent from FIG. 13 since theydeviate in-plane. The general case also applies to describe the rippleorientation, but FIG. 13 does not show first or second routes of fibers130 and 132 since they are superimposed over and could not bedistinguished from the fibers themselves. Although FIG. 13 shows onlyone fiber in each ply, it will be appreciated that plies includeadditional fibers. Rippled first fibers 130 in first ply 138 have afirst composition in common and rippled second fibers 132 in second ply139 have a second composition in common that differs from the firstcomposition.

FIGS. 14 and 15 show a further modification to plies compared to thosein FIG. 12, wherein second fibers do not include ripples or includeripples that deviate to a lesser extent. FIG. 14 shows a side view offirst fiber 140 in a first ply 148 and a second fiber 142 in a secondply 149. Ripples in first fiber 140 deviate from and return to a firstroute 144 within first ply 148. Ripples in second fiber 142 deviate fromand return to a second route 146 within second ply 149. First route 144and second route 146 are substantially parallel. Ripple orientations areas described analogously for FIG. 12. Although FIG. 14 shows only onefiber in each ply, it will be appreciated that plies include additionalfibers. First fibers 140 in first ply 148 have a first composition incommon and second fibers 142 in second ply 149 have a second compositionin common that differs from the first composition. In addition to havinga different composition, ripples in fiber 140 deviate to a lesser extentthan ripples in fiber 142. Specifically, the period of fiber 142 istwice that of fiber 140. For each cycle in ripples of fiber 102, twocycles exist in ripples of fiber 100.

FIG. 15 shows a side view of rippled first fiber 150 in a first ply 158and a second fiber 152 in a second ply 159. Ripples in first fiber 150deviate from and return to a first route 154 within first ply 158.Second fiber 152 does not deviate from a fiber route, instead beingsuperimposed thereon since no ripples are in fiber 152. A route forfiber 152 is thus not shown in FIG. 15 as not distinguishable from fiber152. First route 154 and second fiber 152 are substantially parallel.Ripple orientations are as described analogously for FIG. 12. AlthoughFIG. 15 shows only one fiber in each ply, it will be appreciated thatplies include additional fibers. First fibers 150 in first ply 158 havea first composition in common and second fibers 152 in second ply 159have a second composition in common that differs from the firstcomposition.

FIGS. 14 and 15 incorporate the design consideration of differentcomposition among fibers as well as the design consideration of rippleswith different path lengths. However, it will be appreciated that fibersof the same composition could be used in FIGS. 14 and 15 such that onlythe design consideration of ripples with different path lengths isaddressed.

FIG. 16 is a perspective view of a spherical object with fibers 80 and82 of FIG. 8 aligned along lines of latitude on the sphere. FIG. 16shows that fibers 80 and 82 have different compositions, just as in FIG.8. Also, FIG. 16 shows that fibers 80 and 82 have the same amplitude andperiod as in FIG. 8. Routes 84 and 86 within ply 168 forming the surfaceof the spherical object define a geometric surface, as in FIG. 8. Whileply 88 in FIG. 8 is planar, ply 168 in FIG. 16 is curved. Even so, theripples of fiber 80 are coextensive with a geometric surface defined byfirst routes 84. The ripples of fibers 86 are also coextensive with thegeometric surface. It will be appreciated from the description hereinthat fibers 90 and 92 in ply 98 of FIG. 9 could also be used in aspherical object like that of FIG. 16. In that case, the ripples offibers 90 and 92 would not fully coextend with a geometric surfacedefined by the routes of fibers 90 within ply 98. Instead, the rippleswould deviate outward from the geometric surface.

The configurations of FIGS. 3, 6, and 8-15 incorporate varied designconsiderations including selecting fiber path length, as implementedwith the use of ripples, and selecting mechanical properties, asimplemented with the use of different fiber compositions (and/or fibershapes or manufacturing methods). A further design considerationincludes the degree of adhesion between the fibers and the matrix, asimplemented with the use of different combinations of fiber and matrixcompositions. In the examples of FIGS. 3 and 7, if the matrixencapsulating the fibers to form composite material adheres to thefibers too strongly, then the ripples might not pull out withoutfailing. Then, the kinetic energy absorption afforded by pulling outripples does not occur. Consequently, the degree of adhesion may beselected so that, at a minimum, ripples pull out during an impact event,absorbing kinetic energy before failing.

Largely, matrix composition determines adhesion to a given type of fibermaterial and other mechanical properties, but matrix manufacturingmethods, such as curing processes, may also play a role. Such propertiesare often well-defined for known matrix materials and the mostappropriate known materials to achieve specified design goals may beselected. Conceivably, matrix materials of the same chemical compositioncould exhibit different mechanical properties. Consequently, anyreferences herein to matrix materials of different composition could begeneralized to reference materials of different mechanical properties,such as fiber adhesion, even if matrix composition is the same. Examplesof known matrix materials include thermoplastics, includingthermoplastic polyurethanes, and thermosets, including polyesters,epoxies, and rubber-like materials (lightly cross-linked, likeneoprene), silicones, etc. Others are known as well.

The ductility of the matrix, as determined by composition, alsoinfluences how the ripples pull out of the fiber. In a ductile matrix,the matrix may stretch during an impact while the ripples pull out ofthe fiber before breaking adhesion of fibers with the matrix. It isconceivable that pulling out ripples and plastically deforming thematrix through stretching may be sufficient to absorb some amounts ofkinetic energy without breaking adhesion of fibers with the matrix.

The strength of the matrix, as determined by composition, alsoinfluences how the ripples pull out of the fiber. Instead of breakingadhesion with the fibers, the matrix may shear during the impact whilethe ripples pull out of the fiber and a portion of the matrix remainsadhered to the fiber. Understandably then, pulling out ripples andplastically deforming the matrix through shearing may be sufficient toabsorb some amounts of kinetic energy without breaking adhesion offibers with the matrix. Even so, some portions of a fiber may breakadhesion with the matrix while other portions remain adhered to shearedmatrix portions with the ripples nonetheless pulling out.

Since adhesion varies for different combinations of fiber compositionand matrix composition, the degree of adhesion may be used as a thirddesign consideration. With more adhesion, so long as the fibers do notfail, more kinetic energy may be absorbed. A wide variety of progressivefiber loading modes thus become available. Loads applied to a compositematerial during an impact event may be distributed across multiplekinetic energy absorption mechanisms without breaching the composite.Three possible mechanisms include: 1) pulling out fiber ripples duringthe stretching and/or shearing of the matrix, during the breaking ofadhesion with the matrix, or both, 2) breaking adhesion of fibers withthe matrix or shearing the matrix before fiber failure, and 3) selectinga subset of fibers with a failure strain sufficiently low to fail beforeother fibers fail.

A fourth design consideration includes selecting a lateral and/orthickness region of a composite material for implementing the otherthree design considerations. That is, implementation of the three designconsiderations may be beneficially heterogeneously applied throughout acomposite article, whether within a ply, ply-to-ply, or otherwise acrosslateral and/or thickness regions. Some portions of fibers may be rippledwhile other portions are less rippled or not rippled, fibers withdifferent mechanical properties may be used in selected lateral and/orthickness regions, and matrix adhesion, ductility, and strength may varyin selected lateral and/or thickness regions. For example, while onelength portion of a fiber is rippled to a designated extent, anotherlength portion of the same fiber may be rippled to a lesser extent.Rippling, mechanical properties, and matrix adhesion, ductility, andstrength may be designated in desirable patterns. Rippling, mechanicalproperties, and matrix adhesion, ductility, and strength may bedesignated in desirable combinations of all three considerations orfewer than three considerations. Therefore, energy absorption may becontrolled as a function of location in the composite article.

In keeping with the third mechanism above, fiber failure allowsabsorption of additional kinetic energy beyond plastic deformation afterpulling out ripples. According to the fourth design consideration above,one implementation of controlling energy absorption as a function oflocation involves varying failure strain, a mechanical property,ply-to-ply in a thickness region. Fibers firstly impacted by an objectmight have a lower failure strain such that their failure absorbsadditional kinetic energy while fibers secondly impacted avoid failurewith a higher failure strain. This implementation may be included in themethods and apparatuses described herein such that the firstly impactedfibers, the secondly impacted fibers, or both include fiber ripples forfurther kinetic energy absorption.

In a similar implementation, ripples may pull out of firstly impactedfibers with a higher failure strain while fibers secondly impacted failwith a lower failure strain to absorb additional kinetic energy and toavoid failure of the firstly impacted fibers. This implementation may beincluded in the methods and apparatuses described herein such that thefiber ripples of the firstly impacted fibers absorb additional kineticenergy, but the secondly impacted fibers might or might not includeripples.

In a related implementation, more than two failure strains may be usedto provide a gradient of failure strains either increasing or decreasingas an object impacts fibers in successive plies. Other variations ofusing ripples or not using ripples and using two failure strains orusing more than two failure strains are conceivable to achieve thedesign consideration of controlling energy absorption as a function oflocation. These implementations may be included in the methods andapparatuses described herein.

Behavior of a composite article may be described in three generalcategories. First, impact of an object results in no plastic deformationwith kinetic energy absorbed through the strength and resilience of thestructure. Second, object impact produces plastic deformation, but notbreach of the structure. Third, object impact produces both plasticdeformation and breach. The methods and apparatuses herein apply to thelatter two categories. Significant explanation exists herein regardingavoiding breach by progressive fiber loading. However, even thoughkinetic energy is progressively loaded according to the methods andapparatuses herein, the possibility exists for breach when the loadnonetheless exceeds the strength of the materials.

Consequently, FIGS. 17A, 17B, and 17C explain an additional measure thatmay be used in conjunction with the other methods and apparatusesdescribed herein. In FIG. 17A, a composite 170 includes layers 174 a/174b, which may be individual plies or groups of plies, about to beimpacted by object 172. Composite 170 includes frontside layers 174 adesignated apart from backside layers 174 b by a design boundary 176. Aregion of reduced adhesion may exist at design boundary 176, orfrontside layers 174 a and backside layers 174 b may performdifferently, or both. FIG. 17B shows object 172 impacting frontsidelayers 174 a and traveling through them. In FIG. 17B, the methods andapparatuses described herein for progressively loading the kineticenergy from object 172 may be utilized. For example, layers 174 a, 174b, or both may include rippled fibers.

Rippled fibers may be provided in a first ply as a plurality ofinherently straight first fibers. Individual first fibers have across-sectional shape that is substantially constant along a firstlength portion of the individual first fibers. The first length portionsare aligned along substantially parallel first routes within the firstply. The first length portions are also arranged with first localizedripples in the first length portions that deviate from and return toindividual first routes of respective first length portions. Layers 174a, 174 b, or both may include a second ply parallel to the first ply, aplurality of inherently straight second fibers contained in the firstply or the second ply, and a matrix material at least partiallyencapsulating the first and second plies. Individual second fibers havea cross-sectional shape that is substantially constant along a secondlength portion of the individual second fibers. The second lengthportions are aligned along substantially parallel second routes withinthe respective first ply or second ply. The second length portions arearranged without localized ripples in the second length portions or withsecond localized ripples in the second length portions that deviate fromindividual second routes of respective second length portions to alesser extent than the first localized ripples and return to theindividual second routes. The second routes are substantially parallelto the first routes.

Rippled fibers may instead be provided in a first ply as a plurality ofinherently straight first fibers. Individual first fibers have across-sectional shape that is substantially constant along a firstlength portion of the individual first fibers. The first length portionsof the first fibers are aligned along substantially parallel firstroutes within the first ply. The first length portions are also arrangedwith a first pattern referenced to individual first routes of respectivefirst length portions. Layers 174 a, 174 b, or both may include a secondply parallel to the first ply, a plurality of inherently straight secondfibers contained in the first ply or the second ply, and a matrixmaterial at least partially encapsulating the first and second plies.Individual second fibers have a cross-sectional shape that issubstantially constant along a second length portion of the individualsecond fibers. The second length portions are aligned alongsubstantially parallel second routes within the respective first ply orsecond ply. The second length portions are arranged with a secondpattern referenced to individual second routes of respective secondlength portions in a manner different from the first pattern. The secondroutes are substantially parallel to the first routes. Layers 174 a, 174b, or both may include a means for progressively loading the first andsecond fibers when receiving a sufficient force from kinetic energy.

A kinetic energy absorption method may be implemented in layers 174 a,174 b, or both. The method provides a first ply, a plurality ofinherently straight first fibers contained in the first ply, a secondply parallel to the first ply, a plurality of inherently straight secondfibers contained in the first ply or the second ply, and a matrixmaterial at least partially encapsulating the first and second plies.Individual first fibers have a first length portion providing aplurality of first length portions aligned along substantially parallelfirst routes within the first ply. The plurality of first lengthportions are arranged with first localized ripples in the first lengthportions that deviate from and return to individual first routes ofrespective first length portions. Individual second fibers have a secondlength portion providing a plurality of second length portions alignedalong substantially parallel second routes within the respective firstply or second ply. The plurality of second length portions are arrangedwithout localized ripples in the second length portions or with secondlocalized ripples in the second length portions that deviate fromindividual second routes of respective second length portions to alesser extent than the first localized ripples and return to theindividual second routes. The second routes are substantially parallelto the first routes.

The method includes progressively loading the first fibers and thesecond fibers when the first and second plies receive a sufficient forcefrom kinetic energy by:

irreversibly shearing the matrix material or breaking adhesion of thematrix material to at least a part of individual second fibersaccompanied by plastically deforming or causing failure of the secondfibers; and

irreversibly shearing the matrix material or breaking adhesion of thematrix material to at least part of the first localized ripplesaccompanied by pulling out at least part of the first localized rippleswithout failure of the first fibers.

In the event that progressive loading from one of the methods orapparatuses herein is insufficient to stop object 172, FIG. 17C showsbackside layers 174 b becoming catching layers 178 as they delaminateand release from contact with frontside layers 174 a. By controlling therelease properties at design boundary 176 with a region of reducedadhesion, backside layers 174 b may be released, enabling various energyabsorption mechanisms. For example, shearing the region of reducedadhesion absorbs kinetic energy. Also, the shear performance betweenbackside layers 174 b as it becomes catching layers 178 can becontrolled to allow shearing between such layers. The shearing betweencatching layers 178 promotes free movement of catching layers 178 andadditionally absorbs kinetic energy. As a result, breach of thestructure may be avoided by relying on a mechanism in addition toprogressive loading and other methods and apparatuses herein.

Alternatively, or in addition, a progressive loading concept from themethods and apparatuses herein may be incorporated into backside layers174 b to produce catching layers 178. As one example, frontside layers174 a firstly impacted by an object might have a lower failure strainsuch that their failure absorbs additional kinetic energy while backsidelayers 174 b secondly impacted avoid failure with a higher failurestrain. Object impact may thus release backside layers 174 b, becomingcatching layers 178. The firstly impacted fibers, the secondly impactedfibers, or both may include fiber ripples for further kinetic energyabsorption.

According to one embodiment, a kinetic energy absorptive compositearticle includes a first ply and a plurality of inherently straightfirst fibers contained in the first ply. Inherently straight fibers maybe contrasted with fibers set in a curved form that resistsstraightening. Inherently straight fibers have no set form when in arelaxed state and do not resist straightening. In the present article,individual first fibers have a cross-sectional shape that issubstantially constant along a first length portion of the individualfirst fibers. A substantially constant cross-sectional shape might varyin a de minimis amount along fiber length only to the extent that itremains within accepted manufacturing tolerance of a diameterspecification. The first length portions are aligned along substantiallyparallel first routes within the first ply. The first length portionsare also arranged with first localized ripples in the first lengthportions that deviate from and return to individual first routes ofrespective first length portions.

The present article includes a second ply parallel to the first ply, aplurality of inherently straight second fibers contained in the firstply or the second ply, and a matrix material at least partiallyencapsulating the first and second plies. Individual second fibers havea cross-sectional shape that is substantially constant along a secondlength portion of the individual second fibers. The second lengthportions are aligned along substantially parallel second routes withinthe respective first ply or second ply. The second length portions arearranged without localized ripples in the second length portions or withsecond localized ripples in the second length portions that deviate fromindividual second routes of respective second length portions to alesser extent than the first localized ripples and return to theindividual second routes. The second routes are substantially parallelto the first routes.

Additional features may be implemented in the present article. By way ofexample, the composite article may be an aircraft fuel bladder. Thematrix material may be continuous, that is, the same materialencapsulating both the first and second plies. The individual first andsecond fibers may have a substantially round cross-sectional shape.Substantially round shapes include circular, oval, ovoid, and ellipticalshapes.

The cross-sectional shape of individual first fibers may besubstantially constant along another length portion of the individualfirst fibers. The other length portions of the first fibers may bealigned along substantially parallel other routes within the first ply.The other length portions may be arranged without localized ripples inthe other length portions such that the other length portions arecoextensive with their respective other route. That is, individual firstfibers may have a rippled portion and a straight portion. Havingselected length portions of fibers rippled and selected length portionsnot rippled accommodates designating regions of the composite articlefor absorbing more kinetic energy than other regions in keeping withdescription above.

The first localized ripples may be substantially periodic and have aperiod in common and an amplitude in common among the first fibers. Thesecond fibers may be arranged with second localized ripples that aresubstantially periodic and have a period in common and an amplitude incommon among the second fibers. The period of the second localizedripples may be different from the period of the first localized ripples.

The first fibers may have a material composition in common and thesecond fibers may have a material composition in common that isdifferent from the first fibers' material composition. The first fibersmay exhibit a failure strain in common and the second fibers may exhibita failure strain in common that is different from the first fibers'failure strain.

The first localized ripples deviating from and returning to the firstroutes may be coextensive with a first geometric surface defined by thefirst routes within the first ply. The second fibers may be arrangedwith second localized ripples and the second localized ripples deviatingfrom and returning to the second routes may be coextensive with thefirst geometric surface or may be coextensive with a second geometricsurface defined by the second routes within the second ply.

In the alternative, the first localized ripples deviating from andreturning to the first routes might not fully coextend with a firstgeometric surface defined by the first routes within the first ply. Thesecond fibers may be arranged with second localized ripples and thesecond localized ripples deviating from and returning to the secondroutes might not fully coextend with the first geometric surface andmight not fully coextend with a second geometric surface defined by thesecond routes within the second ply.

The second fibers may be contained in the first ply. In the alternative,the second fibers may be contained in the second ply and not in thefirst ply.

The composite article may further include a backside ply containing aplurality of inherently straight third fibers arranged without localizedripples. The matrix material may at least partially encapsulate thebackside ply. The backside ply may consist of inherently straight thirdfibers arranged without localized ripples. The third fibers may have aconstant failure strain along their lengths. The backside ply mayconsist of third fibers having a constant failure strain.

The additional features that may be implemented in the present articlemay also be implemented in other embodiments herein.

In another embodiment, a kinetic energy absorptive composite articleincludes a first ply and a plurality of inherently straight first fiberscontained in the first ply. Individual first fibers have across-sectional shape that is substantially constant along a firstlength portion of the individual first fibers. The first length portionsof the first fibers are aligned along substantially parallel firstroutes within the first ply. The first length portions are also arrangedwith a first pattern referenced to individual first routes of respectivefirst length portions.

The present article includes a second ply parallel to the first ply, aplurality of inherently straight second fibers contained in the firstply or the second ply, and a matrix material at least partiallyencapsulating the first and second plies. Individual second fibers havea cross-sectional shape that is substantially constant along a secondlength portion of the individual second fibers. The second lengthportions are aligned along substantially parallel second routes withinthe respective first ply or second ply. The second length portions arearranged with a second pattern referenced to individual second routes ofrespective second length portions in a manner different from the firstpattern. The second routes are substantially parallel to the firstroutes.

The article further includes a means for progressively loading the firstand second fibers when the composite article receives a sufficient forcefrom kinetic energy. The sufficient force is high enough to overcome athreshold below which no plastic deformation of the article occurs.Aircraft, spacecraft and other vehicular structures endure a widevariety of forces with no plastic deformation. The methods andapparatuses herein do not necessarily change the ability to endure suchforces, instead changing the nature of deformation beyond the thresholdto absorption of higher levels of kinetic energy rather than breach ofthe structure.

Additional features may be implemented in the present article. By way ofexample, the composite article is an aircraft fuel bladder. Theprogressive loading means may include:

the first pattern having first localized ripples in the first lengthportions that deviate from and return to individual first routes ofrespective first length portions; and

the second pattern having no localized ripples in the second lengthportions or having second localized ripples in the second lengthportions that deviate from individual second routes of respective secondlength portions to a lesser extent than the first localized ripples andreturn to the individual second routes.

The second fibers may be arranged without localized ripples and theprogressive loading means may further include:

a period and an amplitude of the first localized ripples;

a failure strain of the first fibers;

a failure strain of the second fibers; and

a degree of adhesion between the matrix material and the first andsecond fibers. The progressive loading means irreversibly breaksadhesion of the matrix material to at least a part of individual secondfibers accompanied by plastically deforming or causing failure of thesecond fibers. The progressive loading means irreversibly breaksadhesion of the matrix material to at least part of the first localizedripples accompanied by pulling out at least part of the first localizedripples without failure of the first fibers when the first and secondplies receive the force from kinetic energy.

The second fibers may be arranged with the second localized ripples andthe progressive loading means may further include:

a period and an amplitude of the first localized ripples;

a period and an amplitude of the second localized ripples;

a failure strain of the first fibers;

a failure strain of the second fibers; and

a degree of adhesion between the matrix material and the first andsecond fibers. The progressive loading means irreversibly breaksadhesion of the matrix material to at least a part of individual secondfibers accompanied by pulling out at least part of the second localizedripples followed by plastically deforming or causing failure of thesecond fibers. The progressive loading means irreversibly breaksadhesion of the matrix material to at least part of the first localizedripples accompanied by pulling out at least part of the first localizedripples without failure of the first fibers when the first and secondplies receive the force from kinetic energy. The additional featuresthat may be implemented in the present article may also be implementedin other embodiments herein.

In a further embodiment, a kinetic energy absorption method provides acomposite article including a first ply, a plurality of inherentlystraight first fibers contained in the first ply, a second ply parallelto the first ply, a plurality of inherently straight second fiberscontained in the first ply or the second ply, and a matrix material atleast partially encapsulating the first and second plies. Individualfirst fibers have a first length portion providing a plurality of firstlength portions are aligned along substantially parallel first routeswithin the first ply. The plurality of first length portions arearranged with first localized ripples in the first length portions thatdeviate from and return to individual first routes of respective firstlength portions.

Individual second fibers have a second length portion and the pluralityof second length portions are aligned along substantially parallelsecond routes within the respective first ply or second ply. Theplurality of second length portions are arranged without localizedripples in the second length portions or with second localized ripplesin the second length portions that deviate from individual second routesof respective second length portions to a lesser extent than the firstlocalized ripples and return to the individual second routes. The secondroutes are substantially parallel to the first routes.

The method includes progressively loading the first fibers and thesecond fibers when the first and second plies receive a sufficient forcefrom kinetic energy by:

irreversibly shearing the matrix material or breaking adhesion of thematrix material to at least a part of individual second fibersaccompanied by plastically deforming or causing failure of the secondfibers; and

irreversibly shearing the matrix material or breaking adhesion of thematrix material to at least part of the first localized ripplesaccompanied by pulling out at least part of the first localized rippleswithout failure of the first fibers.

Additional features may be implemented in the present method. By way ofexample, the second fibers may be arranged with the second localizedripples and the method may further include pulling out at least part ofthe second localized ripples followed by plastically deforming orcausing failure of the second fibers when the first and second pliesreceive the force from kinetic energy. Individual first fibers may havea cross-sectional shape that is substantially constant along the firstlength portion and individual second fibers may have a cross-sectionalshape that is substantially constant along the second length portion.

The composite article may further include a backside ply containing aplurality of inherently straight third fibers arranged without localizedripples and the matrix material at least partially encapsulating thebackside ply. The progressive loading may further include applying theforce with an object having kinetic energy and catching the object withthe backside layer after it passes through the first and second plies.The third fibers may have a constant failure strain along their lengths.

The additional features that may be implemented in the present methodmay also be implemented in other embodiments herein.

The inventors expressly contemplate that the various options describedherein for individual methods and apparatuses are not intended to be solimited except where incompatible. The features and benefits ofindividual methods herein may also be used in combination withapparatuses and other methods described herein even though notspecifically indicated elsewhere. Similarly, the features and benefitsof individual apparatuses herein may also be used in combination withmethods and other apparatuses described herein even though notspecifically indicated elsewhere.

In compliance with the statute, the embodiments have been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the embodiments are not limited tothe specific features shown and described. The embodiments are,therefore, claimed in any of their forms or modifications within theproper scope of the appended claims appropriately interpreted inaccordance with the doctrine of equivalents.

What is claimed is:
 1. A kinetic energy absorption method comprising:providing a composite article including: a first ply; a plurality ofinherently straight first fibers contained in the first ply, individualfirst fibers having a first length portion providing a plurality offirst length portions aligned along substantially parallel first routeswithin the first ply and arranged with first localized ripples in thefirst length portions that deviate from and return to individual firstroutes of respective first length portions, wherein the first localizedripples are substantially periodic and have a period in common with eachother and an amplitude in common with each other; a second ply parallelto the first ply; a plurality of inherently straight second fiberscontained in the first ply or the second ply, individual second fibershaving a second length portion providing a plurality of second lengthportions aligned along substantially parallel second routes within therespective first ply or second ply and arranged without localizedripples in the second length portions or with second localized ripplesin the second length portions that deviate from individual second routesof respective second length portions to a lesser extent than the firstlocalized ripples and return to the individual second routes, the secondroutes being substantially parallel to the first routes; and a matrixmaterial at least partially encapsulating the first and second plies;and progressively loading the first fibers and the second fibers whenthe first and second plies receive a sufficient force from kineticenergy by: irreversibly shearing the matrix material or breakingadhesion of the matrix material to at least a part of individual secondfibers accompanied by plastically deforming or causing failure of thesecond fibers; and irreversibly shearing the matrix material or breakingadhesion of the matrix material to at least part of the first localizedripples accompanied by pulling out at least part of the first localizedripples without failure of the first fibers.
 2. The method of claim 1,wherein the second fibers are arranged with the second localized ripplesand the method further comprises pulling out at least part of the secondlocalized ripples followed by plastically deforming or causing failureof the second fibers when the first and second plies receive the forcefrom kinetic energy.
 3. The method of claim 1, wherein: the compositearticle further comprises a backside ply containing: a plurality ofinherently straight third fibers arranged without localized ripples; andthe matrix material at least partially encapsulating the backside ply;and the progressive loading further comprises applying the force with anobject having kinetic energy and catching the object with the backsideply after it passes through the first and second plies.
 4. A kineticenergy absorptive method comprising: arranging a plurality of inherentlystraight first fibers in a first ply, individual first fibers having across-sectional shape that is substantially constant along first lengthportions of each of the individual first fibers, the first lengthportions being aligned along substantially parallel first routes withinthe first ply and arranged with first localized ripples in the firstlength portions that deviate from and return to individual first routesof respective first length portions, wherein the first localized ripplesare substantially periodic and have a period in common with each otherand an amplitude in common with each other; arranging a plurality ofinherently straight second fibers in the first ply or in a second ply,individual second fibers having a cross-sectional shape that issubstantially constant along a second length portion of the individualsecond fibers, the second length portions being aligned alongsubstantially parallel second routes within the respective first ply orsecond ply and arranged without localized ripples in the second lengthportions or with second localized ripples in the second length portionsthat deviate from individual second routes of respective second lengthportions to a lesser extent than the first localized ripples and returnto the individual second routes, the second routes being substantiallyparallel to the first routes; and at least partially encapsulating thefirst and second plies in a matrix material.
 5. The method of claim 4,wherein the individual first and second fibers have a substantiallyround cross-sectional shape.
 6. The method of claim 4, wherein thecross-sectional shape of individual first fibers is substantiallyconstant along other length portions of the individual first fibers, theother length portions of the first fibers being aligned alongsubstantially parallel other routes within the first ply and arrangedwithout localized ripples in the other length portions such that theother length portions are coextensive with their respective other route.7. The method of claim 4, further comprising: arranging second fiberswith second localized ripples that are substantially periodic and have aperiod in common with each other and an amplitude in common with eachother, the period of the second localized ripples being different fromthe period of the first localized ripples.
 8. The method of claim 4,wherein the first fibers have a same material composition and the secondfibers have a same material composition that is different from the firstfibers' material composition.
 9. The method of claim 4, wherein thefirst fibers exhibit a same failure strain and the second fibers exhibita same failure strain that is different from the first fibers' failurestrain.
 10. The method of claim 4, wherein the first localized ripplesdeviating from and returning to the first routes are coextensive with afirst geometric surface defined by the first routes within the firstply.
 11. The method of claim 10, further comprising: arranging thesecond fibers with second localized ripples and the second localizedripples deviating from and returning to the second routes that arecoextensive with the first geometric surface or are coextensive with asecond geometric surface defined by the second routes within the secondply.
 12. The method of claim 10, wherein the first localized ripplesdeviating from and returning to the first routes do not fully coextendwith a first geometric surface defined by the first routes within thefirst ply.
 13. The method of claim 4, wherein the second fibers arearranged in the first ply.
 14. The method of claim 4, wherein the secondfibers are arranged in the second ply and not in the first ply.
 15. Themethod of claim 4, further comprising: arranging a plurality ofinherently straight third fibers without localized ripples in a backsideply; and at least partially encapsulating the backside ply in the matrixmaterial.
 16. A kinetic energy absorptive method comprising: aligning aplurality of first fibers aligned along substantially parallel firstroutes within a first ply; arranging the plurality of first fibers withfirst ripples that deviate from and return to individual first routes ofrespective first fibers, wherein the first ripples are substantiallyperiodic and have a period in common with each other and an amplitude incommon with each other; arranging a plurality of second fibers containedin the first ply or in a second ply without ripples or with secondripples that deviate from individual second routes of respective secondfibers to a lesser extent than the first ripples and return to theindividual second routes, the second routes being substantially parallelto the first routes; and at least partially encapsulating the firstfibers and second fibers in a matrix material.
 17. The method of claim16, wherein second fibers are arranged with second ripples that aresubstantially periodic and have a period in common with each other andan amplitude in common with each other, the period of the second ripplesbeing different from the period of the first ripples.
 18. The method ofclaim 16, wherein the first fibers have a same material composition andthe second fibers have a same material composition that is differentfrom the first fibers' material composition.
 19. The method of claim 16,wherein the first fibers exhibit a same failure strain and the secondfibers exhibit a same failure strain that is different from the firstfibers' failure strain.
 20. The method of claim 16, wherein theindividual first and second fibers have a substantially roundcross-sectional shape.